1. Field of the Invention
The invention relates to the clipping of audio signals in the digital domain.
2. Prior Art
Audio signals are frequently clipped at a positive and a negative threshold particularly in the broadcast field to prevent overmodulation of the transmitter, which is ordinarily defined by government regulation. In most instances, the “clippings” (that is the signal that remains above or below a threshold) are used in subsequent processing. Sometimes, even when some subsequent processing is done in the digital domain, the clipping itself is performed in the analog domain. Simple clipping in the digital domain (defined as setting to the positive or negative threshold of clipping any sample that exceeds the respective threshold of clipping) introduces additional distortion in the form of aliasing and jitter, thus the use of clipping in the analog domain has persisted.
The use of “clippings” for signal processing is described in U.S. Pat. No. 5,737,434 entitled “Multi-Band Audio Compressor with Look-Ahead Clipper” and U.S. patent application Ser. No. 09/216,345, filed Dec. 18, 1998, entitled “Oversampled Differential Clipper.”
If the subsequent processing of the “clippings” consists only of linear operations like summation and linear filtering (which is typically true), it should be particularly noted that anti-aliasing the “clippings” then completely anti-aliases subsequent processing using the “clippings,” because the “clippings” contain all of the non-linear spectrum added by this processing to the unprocessed signal.